I can't take full credit for this. I saw my sister-in-law Elizabeth do this a couple years ago and I tucked it away in my mind. This project will take between 30 to 60 minutes, depending on your skill level and the amount of embellishing you do. This is a good project for a beginner. 

Supplies:

• t-shirt
• coordinating knit fabric (I used another shirt that I was okay with cutting up)
• thread
• needle
• scissors
• pins
• sewing machine

Cut circles from your embellishing fabric. For my t-shirt, the largest ones I used were 3+ inches in diameter. For Greta's, they were about 1 inch and Holly's were a little bigger than that. I like to have varying sizes to work with. 

Fold each circle into quarters and, with a hand needle, stitch a small square at the end, using coordinating thread (I used dark thread so it would photograph). You don't want your stitch to be too big. Mine were about 1/8th to 1/4 of an inch. Remember to start and finish with a knot.

Open your "rosettes" up and arrange them on your shirt. I choose to do a bib style for my shirt. And I like to layer the rosettes.

Pin like crazy. Make sure your pins are perpendicular to the direction you'd like to sew.

Sew the rosettes on using a sewing machine. I pivoted at the edges, so my stitching was continuous. Remove pins as you go.

Take a look and add in any more stitching as necessary (to flopping edges, etc). Admire your handiwork and wear!

Side note: Embellishing is a great way to resurrect a shirt. I had a shirt, which I loved, but it had some small bleach stains on it, so it was hanging in my closet without being worn. I covered those bleach stains up using this method and it's now a favourite again!